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A Hybrid Species

In this video from the PBS series NATURE, students are introduced to the coywolf, a new species that is a hybrid between a coyote and a wolf. Dr. Roland Kays of the New York State Museum compares skulls from the museum's mammal collection to show the anatomical differences between the coywolf and its parent species.

Ancient Greece was filled with stories of hybrids—centaurs, griffins, mermaids, and the Pegasus among others. Each of these mythological creatures combined the physical traits of two different species. While none of these creatures actually existed, the natural world is filled with real animal hybrids*.

A hybrid is an organism that has parents from two different species. The most familiar example of an animal hybrid is probably the mule, a cross between a female horse and a male donkey. Lesser known hybrids include the beefalo, a cross between a bull and a female bison, the liger, a cross between a male lion and a tigress, and the wholphin, a cross between a false killer whale and a dolphin.

Hybridization between animal species is relatively rare. Even if two species are theoretically capable of producing hybrids, they may have different mating rituals, breeding seasons, and geographic territories. Certain species also have immune responses to prevent fertilization by the sperm of another species.

When members of different species do produce offspring, they are often sterile. Sterility in hybrid animals can be caused by differing numbers of chromosomes in the parent species. For instance, horses and donkeys have 64 and 62 chromosomes respectively, leaving mules with 63. These chromosomal differences make it difficult, if not impossible, for many hybrid animals to reproduce. Even when hybrids are fertile, they may find themselves competing with their parent species for resources, and if they don’t inherit the traits necessary to succeed in their environment, they are at an even further disadvantage. Thus, hybrid animals do not usually give rise to new species.

* The term "hybrid" has many different definitions in both biology and taxonomy. In this essay, the word "hybrid" is used to describe any organism with parents from two different species.

Before starting the video, review the definition of the word 'species' (a group of organisms that are able to mate with each other and produce fertile offspring). Explain that they will be learning about a new North American species that has emerged in the past 100 years.

As an extension, have students research and present on other hybrid animals. Make sure they include whether the animals constitute a separate species and what adaptations set them apart from their parent species.

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Funder:Major support for NATURE is provided by the Arnhold Family, in Memory of Clarisse Arnhold, the Lillian Goldman Charitable Trust, and the Filomen M. D’Agostino Foundation. Support is also provided by the Corporation for Public Broadcasting, and PBS.